Grading sieving machines

In mechanical process technology, classification or grading describes the separation of solid mixtures according to particle sizes. The objective of grading is to divide the screening material into at least two fractions, where ideally each group corresponds to the provided size criteria as closely as possible. The number of fractions wanted varies from task to task. In many cases, the largest and the smallest particle sizes are separated off as they are classed as ‘out of place’ particles. The correctly sized particles can then be graded further into different particle sizes as needed. With grading sieving machines from Engelsmann, up to 8 different fractions can be screened off.

The JEL VibRS can be used for separating up to 6 fractions. Thanks to screen decks which can be stacked on top of each other, even large screening surfaces can be set up on a small surface.» Further information

The highly versatile long-stroke screening machine JEL Phoenix combines a screening process which is particularly gentle on the product with the highest screening precision and optimal screening and energy efficiency.» Further information

Used for separating coarse and fine particles as well as for grading, the JEL VibSpeed will win you over with its many cleaning facilities.» Further information

The most important criteria when grading: The selectivity

The so-called selectivity is the most important criteria when it comes to grading and the machine used. This determines how precisely the individual fractions will be separated from one another. With grading sieving machines, the selectivity should ideally be 100%. However, with industrial grading, a selectivity of one hundred percent can only be approximated in practice. The degree of selectivity will be influenced mostly by the movement of the screen and the dwell time of the product on the screen mesh.

How can I achieve high selectivity during grading?

Screen movement and dwell time

With the grading sieving machines from Engelsmann, the product can be graded very selectively (up to 99%). This is mainly because the vibration and oscillation amplitude as well as the screen inclination are adjustable. As a result, the intensity of the screen movement, and therefore also the dwell time of the product on the screen mesh, can be influenced and perfectly adjusted to the product which is to be graded. For example, poorly flowing or sticking products require the screen inclination and oscillation amplitude to be adjusted in a different way than if it was for an easilyflowing solid in order to make it move on the screening surface.

Because of their linear movement, long-stroke sieving machines guarantee a very selective grading. Thanks to the solely horizontal movement of the screen, the product always remains in contact with the screen and does not jump up and down. In addition, the dwell time of the screened product on long-stroke screening machines can be easily increased by placing several screen inserts with the same mesh size behind or on top of one another. Thus increasing the course that the product must cover on the screen surface.

Optimal product distribution

An optimal distribution of the product on the screen mesh also has a positive influence on the selectivity of the grading, therefore Engelsmann grading sieving machines can be fitted with a separator sheet or bar. This distributes the product over the entire screening surface after it is fed into the sieving machine so that the screened product doesn’t build up too much on the screen mesh beneath the inlet nozzle. This ensures that during the grading, the product being screened is always in complete contact with the screening surface and can be optimally screened off.

Custom-fit covered screen inserts

Precisely covered screen inserts also play an important role when it comes to grading, as they also influence on how selective the screening result is. If the mesh is not evenly covered, the individual meshes can sag or warp. Inserts with non-homogenous mesh sizes inevitably lead to poor screening results during grading. Thanks to Engelsmann’s internal testing procedure, screen inserts can be measured after covering, in accordance with DIN ISO 9044 and DIN ISO 3310-1, and the homogeneity of the screen mesh can be checked. Customers that buy a screening machine or replacement screen insert from Engelsmann can also receive a corresponding test report upon request and therefore increase process safety.

What spectrum of particle sizes are graded in practice?

The grading can be carried out with various products and particle sizes in practice. The range of applications of the grading sieving machines from Engelsmann ranges from dust particles with a diameter of just 40 μm, up to coarse products with a diameter of 20 mm.